A digital multimeter (DMM) is an electronic test instrument that measures electrical current in a wire without the need to electrically isolating the wire. Such multimeters are typically used to measure a variety of electrical parameters, such as voltage, resistance and current. Clamp-type DMMs, also known as “clamp meters”, measure current in a conductor without having to make an electrical connection with a circuit. Instead, such DMMs include two clamp jaws having embedded electrical coils. In use, the jaws are clamped onto a conductor and measure the current within the conductor.
If the conductors are bundled together in a tight physical space, such as an electrical cabinet, it is often difficult to insert the clamp meter into the small area to measure an individual wire. As such, it is desirable to size the jaws of the clamp meter to fit within tight spaces. One way to reduce the size of the jaws is to minimize any space between the jaw core and the housing that surrounds the jaw core. However, reducing the space between the housing and the core can lead to safety issues.
The international standard for test equipment safety, IEC 61010-1, requires a minimum creepage and clearance path between the outside of the jaw housing and the nearest metallic part or circuit board inside the instrument, which is typically the jaw core. “Clearance” is the shortest distance through the air between two conductive elements. In this case, the first conductive element would be a user's hand disposed on the exterior of the housing, and the second conductive element would be the core disposed within the jaw. “Creepage” is the shortest distance along the surface of the insulative material between two conductive elements. The interior of the housing and the core are typically separated from each other by air and/or an insulative material. Reducing the air gap or the thickness of the insulative material decreases the overall size of the jaw, but it would also reduce the creepage and clearance path and would violate safety standards.
One known solution for reducing the overall size of the jaw of a clamp meter without reducing the clearance and creepage path includes covering at least a portion of the jaw core with an insulating tape. The tape increases the clearance path along the jaw core without adding any distance between the jaw core and the jaw housing. Although effective, the tape needs to be manually applied to the curved surfaces of the jaw core, which is time consuming and difficult to apply. Often the tape is applied unevenly and it can crease or wrinkle when adhered to a curved surface. Creases, wrinkles, and uneven application of the tape can decrease the creepage and clearance path, thereby violating safety standards and putting a user at risk. Accordingly, there is a need for a safe, easy method of increasing the creepage and clearance path in a clamp meter jaw assembly.